Flexible circuit carriers consist of a flexible, thin polymer foil with a structured metallization layer as conducting paths. The flexible circuit carriers can be either single-layer or multilayer. Multilayer flexible circuit carriers are provided with contact channels, so-called plated-through holes, which are arranged at right angles to the layers and which connect the individual levels electrically.
Flexible circuit carriers are employed where parts of a system which are movably connected to one another are electrically connected. Examples of this are notebooks or laptops with a hinged screen and collapsible mobile telephones. In the automobile industry, flexible circuit carriers are needed e.g. so that electrical connections entering the engine area can be decoupled from mechanical vibrations, Where space is severely restricted in a geometrically complex housing, circuits implemented on flexible circuit carriers can be matched to the shape of the housing in a space-saving way (3-dimensional design), something that is not possible with rigid printed circuit boards (2-dimensional design).
A bonding technique of the first level (first-level bonding technique) between one or more chips and a flexible circuit carrier is the so-called tape automated bonding (TAB) To realize the advantage of a high number of connections per chip surface, so-called flip-chip technologies have also been used on flexible circuit carriers very recently. Patent Abstracts of Japan, Vol. 9, No. 284 (E-357), Nov. 2, 1985 discloses a method for connecting a flexible substrate to bonding areas of a semiconductor element. In this method the conducting paths on the flexible circuit are each connected with bonding areas of the semiconductor element using a metal ball and compression bonding.
From DE 4131413 A1 a bonding method for semiconductor chips is known wherein a first gold ball, a second gold ball and a lead ball are used per bonding site to apply a chip to a substrate by means of a flip-chip bonding method.